Coin discriminators are used for measuring different physical characteristics of a coin in order to determine its type (e.g. its denomination, currency or authenticity). Various dimensional, electric and magnetic characteristics are measured for this purpose, such as the thickness and diameter of the coin, its electric conductivity and its magnetic permeability. Coin discriminators are commonly used in coin handling machines, such as coin counting machines, coin sorting machines, vending machines, gaming machines, etc. Examples of previously known coin handling machines are for instance disclosed in WO97/07485 and WO87/07742.
Starting with the electric characteristics of coins, EP-B-300,781 and EP-B-0,119,000 describe previously known ways of measuring coin conductivity. A transmitter coil is driven with a pulsed supply voltage so as to generate a magnetic pulse, which is induced in a coin, which moves along a coin path or rail past the transmitter coil. The eddy currents thus generated in the coin in turn produce a magnetic field, which is monitored or detected by a receiver coil. The receiver coil may be a separate coil or may alternatively be constituted by the transmitter coil itself having two operating modes. By monitoring the decay of the eddy currents induced in the coin, a value representative of the coin conductivity may be obtained, since the rate of decay is a function thereof. A coin discriminator of a similar type, albeit especially adapted for bimetallic coins, is disclosed in WO99/39311.
As regards the magnetic characteristics of coins, e.g. their magnetic permeability, U.S. Pat. No. 4,483,431 relates to a coin discriminator, where a permanent magnet and a Hall effect device is used for checking the magnetic properties of the coin, when it passes the Hall effect device. Moreover, U.S. Pat. No. 5,119,916 discloses a sensor for validating subway tokens. The sensor has two pairs of permanent magnets and Hall effect sensors, which determine the magnetic characteristics (and consequently the permeability) of the respective token.
Various methods are known for determining the coin diameter in coin discriminators. According to PCT GB88/00592 a coin is exposed to high-frequency magnetic pulses from a pair of coils. When the coin passes the coils, the magnetic field is shielded, and a pickup coil is used for determining the coin diameter in response to this momentary shielding. Alternatively, the coin diameter may be determined optically by using a line of optical detectors located opposite a light source. When a coin passes between the optical detectors and the light source, a certain number of the optical detectors are momentarily shielded or cut off by the passing coin. The coin diameter follows immediately from the number of shielded optical detectors.
Also the coin thickness may be determined by optical arrangements similar to the one described above for measuring the coin diameter. Alternatively, as disclosed in EP-B-300,782, an ultrasound detector may be used for determining the thickness of a coin. Furthermore, EP-A-343,871 discloses a capacitive coin validation method, involving a pair of electrode assemblies on either sides of a coin path. Most specifically, in EP-A-343,871 the pair of electrode assemblies comprises sensor electrodes and guard ring electrodes that are disposed on either sides of the coin path. The sensor electrodes are driven with an oscillating signal from dual resonant circuits, so that when a coin passes the electrodes during the validation thereof, the inter-electrode capacitance is altered. Thus, in effect, the sensor electrodes act as first and second capacitor plates that form a capacitor, the capacitance of which is changed by the presence of the coin. Thereby, also the resonating signals from the resonant circuits are changed. In EP-A-343,871, the coin must be electrically isolated from the electrode assemblies, thereby requiring electrical isolation in the coin path.
Thus, the device in EP-A-343,871 requires an electrically isolated coin path and, moreover, first and second capacitor plates (the electrode assemblies) placed on either side of the coin path.